1. Field of the Invention
This invention relates generally to a distance device and more particularly to a distance measuring device designed to detect the distance to an object by the combined use of a radiant ray (or infrared ray) projecting element and a signal storage type radiant ray (infrared ray) sensor. The result is a detection suitably usable, for example, for automatic focusing control over the photo-taking lens of a camera or the like.
2. Description of the Prior Art
Heretofore, various methods have been proposed and put into practice for distance measurement. Of these methods, methods of the passive type in which the distance is measured by detecting a change of a double image into a single image or the contrast of an image based on a light emitted by a distance measuring object the distance of which is to be measured have presented a problem in that the distance measuring performance of such a device decreases when the brightness of the object is low.
Meanwhile, active methods in which radiant rays, such as a light, are projected on the distance measuring object and the distance to the object is measured on the basis of light reflected by the object give a high degree of distance measuring performance. However, the active methods necessitate the use of a mechanical sweep system and also require some arrangement for keeping an electrical signal processing system at a high S/N ratio. A typical example of such methods is a device of the type in which the object is swept with a projection light to create a reflected light which is then received from the object by a light sensitive element and the distance is obtained from the sweep angle of the projection light at which the quantity of reflection light received by the light sensitive element becomes a maximum value, that is, where the maximum output of the light sensitive element is obtained. In this type of arrangement, it is absolutely necessary to carry out a sweep with the projection light. This tends to result in a complex mechanical structure. Further, in order to detect the maximum value of the output of the light sensitive element, use of a peak detection circuit or the like is, in general, necessary. The use, however, of a peak detection circuit is inevitably accompanied a time lag. The time lag makes correlation between the sweep angle .theta. of the projection light and a peak detection point of time hard to obtain. This degrades the accuracy of distance detection.
In another example of the conventional methods, the arrangement which sweeps with the projection light is replaced with an arrangement in which the projection angle of the projection light is fixed, a plurality of light sensitive elements are arrayed behind a light receiving optical system, and the distance is measured by determining which light sensitive element receives the reflection light to the greatest degree. Such a method, however, necessitates provision of a light receiving amplifier and a demodulator for every light sensitive element employed and thus tends to result in a complex structure which is difficult to adjust. Such a method, therefore, presents a problem in terms of economy.